1. Field of the Invention
The present invention relates to rocket engine combustion chamber fabrication and more particularly to a rocket engine combustion chamber having multiple conformal throat supports.
2. Description of the Related Art
The function of a rocket engine combustion chamber is to contain the combustion process (typically at 5000xc2x0 F. to 6000xc2x0 F. at 1000 to 4000 pounds per square inch pressure) and then accelerate the combustion products to a high velocity and exhaust them to create thrust. Typically, the combustion process takes place subsonically in the combustion chamber. The subsonic combustion gases are then accelerated supersonically through a converging/diverging DeLaval-type nozzle/venturi.
The combustion chamber typically includes a structure to contain the combustion pressure, a cooled liner to protect the pressure vessel from the hot combustion gases, and manifolding required to circulate the coolant. Because of its inherent hourglass shape, combustion chambers are typically fabricated by starting with the coolant liner and building the pressure vessel jacket and manifolding around its external hourglass contour or starting with the pressure vessel and manifolding structure and building the coolant liner inside its internal hourglass contour. Materials of construction typically consist of copper base alloys for the coolant liner because of their high thermal conductivity and nickel-base alloys for the pressure vessel jacket and manifolds because of their high specific strength.
Currently, there are several methods of making combustion chambers with coolant channels. All of the methods in use today involve many fabrication steps each of which require critical inspections and possible rework if flawed. These processes are time consuming and expensive.
In one method, a coolant liner is machined from a billet of material with the inner and outer hourglass shape. Coolant passage slots are machined on the outer surface of the liner. The coolant passages are then closed out using a plating process. The plating process is very labor-intensive, requiring several critical operations and is fraught with problems which can cause a considerable amount of rework in a typical chamber.
During the channel closeout process, the liner slots are filled with a wax material. The outer exposed surface is then burnished with a silver powder which forms a conductive plateable surface. On that surface, a hydrogen barrier may be plated as applicable, which is then followed by plating a build up of nickel to form a structural closeout to contain the coolant pressure. The nickel close out requires several plating cycles and several intermediate machining steps. All of the plating operations are subject to problems such as contamination, plating solution chemistry, and other process parameters that can lead to poor bonding of the plated material. If an anomaly occurs during this process, the plated material on the liner has to be machined back and the plating process repeated. Using this technique requires considerable time and labor to close out a liner.
Following the plating operations, the wax material must then be removed from the liner. This is a critical process, since any residual wax material can lead to contamination problems in subsequent operations.
When the liner is completed, the next step is to weld the inlet and outlet coolant manifolds to the liner structure. Local areas on the liner need to be built up with a considerable amount of electrodeposited nickel and machined backed to form a surface that can accommodate the weld joints. The manifolds are then welded onto the closed-out liner. Then the structural jacket, which is made up of several pieces, is assembled around the outside of the liner and manifold subassembly and welded in place. All of the weld joints are critical and require inspections. Any flaws found must be reworked. A typical combustion chamber may require as many as 100 critical welds. The process is very costly and time consuming. Utilizing this process, a complete main combustion chamber can take three (3) years to fabricate.
Another main combustion chamber fabrication method utilizes a xe2x80x9cplateletxe2x80x9d liner concept. In this method, the liner itself is made up of a stack of several very thin plates which are photochemically etched to form coolant slots, individually plated, stacked together, and then bonded to form a flat panel section of the liner with closed-out coolant passages. The flat panels are then formed to make up a section of the hour-glass shape liner. One of the plating processes or the bonding processes can result in a joint failure during the forming process a bad joint, which would be reason to scrap the part. Typically seven or more individual panels are required to form an hourglass-shaped liner. The individual panels are installed inside the structural jacket. Since a longitudinal joint is required between each of the adjacent panels, there are several locations for potential hot-gas leakage between the panels along the entire length of the combustion chamber. Also, all of the panels once installed, have to be bonded to the outer structural jacket. In order to bond the panels to the outer structural jacket, pressure bags are fabricated to match the contour of the thrust chamber. The bags are installed inside the thrust chamber liner along with backup tooling to support the pressure bags. The chamber and tooling are placed into a brazing furnace and brought up to temperature while the pressure is maintained in the pressure bags, which forces the liner into intimate contact with the jacket to create a bond joint a bond joint between the closed-out liner and the structural jacket. Pressure bags have not been 100% reliable since they can burst or leak, and it is very difficult to fabricate and maintain the correct geometry of a thin conformable pressure bag that will match the complex geometry of the combustion chamber liner and still contain the pressure required at bonding temperature.
U.S. Pat. No. 5,701,670, issued to Fisher et al. discloses a method of making a rocket engine combustion chamber utilizing a xe2x80x9cslide inxe2x80x9d port liner. The ""670 invention utilizes three basic components to form a combustion chamber for high-performance rocket engines: (1) a structural jacket, (2) a single-piece coolant liner, and (3) a plurality of throat support sections. The combustion chamber fabrication is described in the following steps. A liner is machined which has coolant channels formed in the outer surface. Throat support sections are fabricated and assembled around the indentation created by the venturi shape of the combustion chamber liner. The throat supports and the liner are then slid into the structural jacket. A welded or brazed seal joint between the liner and the structural jacket is made at the both forward and the aft end of the chamber. Any access ports to the coolant manifold system are closed off for the HIP bond cycle. The coolant passages and voids between the throat support sections and the structural jacket are thus sealed off from the outside environment. The entire assembly is then placed into a furnace. The furnace is pressured and then brought up to bonding temperature. To aid in the bonding process, a vacuum may be drawn on the coolant passages and the void in the throat support area. At temperature, with the pressure applied to the entire outer surface of the jacket as well as the inner surface of the liner, the liner is forced to conform to the structural jacket and throat support contour, resulting in intimate contact at all the braze interfaces. At pressure and temperature, with intimate contact between the four parts, a bond joint is created between the liner and the structural jacket. Bond joints are also formed between the liner and the throat support sections, between the throat support sections themselves, and between the throat supports and the structural jacket. All of the bonding is done in one step in the pressurized furnace without requiring special tooling to force the parts into intimate contact. This method of fabrication closes out the coolant liner channels without having to utilize complicated wax filling, silver burnishing, electroplating, and machining process steps which have caused considerable problems in the past. Once the bonding is complete, the seal joint at the forward and aft end of the chamber is no longer required and may be removed from the assembly. The method eliminates all welds from the finished part. The invention is an improvement over past processes because there are no welds, there is no structural plating, and the critical liner is completely fabricated from a single piece of metal thus eliminating any joints required to form coolant channels. Further, there are no joints to be sealed longitudinally or anywhere else in the hot gas wall of the liner. The invention uses an integral liner that is machined from a single piece, which forms a barrier to isolate the hot gas from the structural jacket and preclude the coolant from leaking out into the hot gas which can cause a lack of coolant for the structural jacket. The resultant part, however, is heavier than those using the manufacturing techniques described earlier in this Description of the Related Art. Although, methods exist to reduce weight at the end of the process, all such methods have risk and all add cost. Additionally, the structural jacket may be structurally inefficient owing to the requirement to be compatible with the HIP braze process. Finally, the process potentially introduces the high pressure coolant gas in the liner to intimate contact with the structural jacket.
In a broad aspect, the present invention comprises a method of fabricating a rocket engine combustion chamber including a number of assembly steps. A coolant liner is formed having an outside surface. A plurality of coolant channels are formed on the outside surface. At least two inner conformal throat support sections and at least two outer conformal throat support sections are formed. The two inner conformal throat support sections are installed around the outside surface of the coolant liner to form a closed inner conformal throat outside surface. The inner conformal throat support sections are joined at longitudinal inner throat seam lines. At least two outer conformal throat support sections are then assembled around the closed inner conformal throat outside surface so as to cover the inner throat seam lines, to form a liner throat support assembly. An inlet manifold and an outlet manifold are assembled around the liner throat support assembly to form a hot isostatic press (HIP) assembly. A HIP""ed assembly is formed by HIP""ing the HIP assembly. Fabrication costs are minimized by obviating any requirement of a structural jacket during HIP""ing. Weight is minimized as a result of utilizing the inner and outer conformal throat supports.
Other objects, advantages, and novel features will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.